1. Field of the Invention
The present invention relates to a photo resist used for fine processing of a semiconductor, a photo mask blank, and so forth, in particular, a resist patterning process with regard to a chemically-amplified type resist used in a KrF excimer laser, an EUV, and an electronic beam, and a method for manufacturing a photo mask.
2. Description of the Related Art
It is well known that, as LSI progresses toward a high integration and a further acceleration in speed, a miniaturization of a pattern rules is required. With this trend, an exposure method and a resist composition have been largely changed, and in particular, when performing a lithography of a pattern with 0.2 micrometer or less, a KrF or an ArF excimer laser or an electronic beam, and the like are used as a light source, while an EUV is about to be used for a pattern rule with less than 30 nanometers. Because, in a photo resist used in a lithography method like this, a good sensitivity to such high energy beams as mentioned above is necessary, a number of chemically-amplified types giving a high sensitivity and a high resolution power have been developed.
Among these photo resists, various kinds of a base polymer to form a resist pattern used in a positive resist have been proposed. A positive resist having been actually used is based on a mechanism with which it is made soluble into an alkaline developer by eliminating an acid-labile protecting group, which protects an acidic functional group at side chain of a base polymer, by an acid as its catalyst that is generated by exposing a high energy beam to an acid generator. Accordingly, a molecular weight of a base polymer added in a resist composition does not change before and after a light-exposure.
On the other hand, control of a resist pattern profile is based on whether or not dissolution properties of polymers in a resist film after the light-exposure can be controlled at a micro level. Accordingly, from a considerably early stage of practical use of a chemically-amplified resist, control of the molecular weight dispersion of a base polymer has been drawing an attention (Japanese Patent Laid-Open Application No. H5-132513).
Although prior patents and the like mentioned various aspects of the molecular weight of a base polymer, when a base polymer of polyhydroxystyrene is actually used, the weight-average molecular weight (Mw) of about 8,000 to 15,000 has been generally used. In fact, in the case of a resist using an acetal-protected polyhydroxystyrene, the one with Mw of about 5,000 showed a tendency to form a resist pattern with a round head rather than a rectangular head, and the one with too large Mw, for example 20,000 or more, showed a tendency to leave behind a scum caused by re-adhering of a dissolved or partly-dissolved polymer after dissolution.
As to a base polymer obtained by radical polymerization of polyhydroxystyrene, an acrylic acid derivative protected by an acid labile group, and further a unit not dissolvable in an alkaline developer such as styrene, for example, a use of a base polymer slightly larger than a comparative example of polyhydroxystyrene is disclosed in Japanese Patent Laid-Open Application No. H7-209868.
However, in the development of a photo resist using an acrylic acid type polymer, it was found that a considerably large amount of scum were formed in the case of Mw of about 10,000, if a conventional method was followed. Accordingly, as disclosed in Japanese Patent Laid-Open Application No. 2008-122932 and so forth, Mw of about 5,000 to 9,000 are generally used in many cases.
A resist using a base polymer, which is a copolymer of hydroxystyrene and a cycloolefin containing an aromatic ring and is insolubilized into an alkaline developer by protecting with an acetal protecting group, proposed by inventors of the present invention (for example, Japanese Patent Laid-Open Application No. 2007-132998, Japanese Patent Laid-Open Application No. 2008-95009, and so forth), is a useful photo resist having high resolution and etching resistance. The resist disclosed there had Mw of specifically about 9,000 to 15,000, and yet they showed no problem of the scum as mentioned above.
Resist compositions disclosed in Japanese Patent Laid-Open Application No. 2007-132998, Japanese Patent Laid-Open Application No. 2008-95009, and so on are useful materials to form fine patterns especially by a high energy beam such as an electronic beam and an EUV, and its important application is for processing of a photo mask blank. A circuit drawn on a photo mask is projected with a reduced size by one-fourth in a exposure. However, this does not mean that a line width of the mask pattern may allow to be 4-folds relative to an intended pattern rule, and it is processed to a more complicated pattern (a pattern applied with a so-called OPC, Optical Proximity Correction, and the like) than an actual circuit pattern in order to correct a light diffraction and the like. Accordingly, in a mask processing to manufacture a semiconductor having, for example, a 45 nanometers pattern rule, eventually a resist to resolve a 45 nanometers pattern is necessary. For this reason, further improvement of a resist to manufacture a photo mask to resolve a pattern with 45 nanometers or less is desired.